The invention relates generally to power-driven conveyors and, more particularly, to conveyor systems having conveyor belts with object-supporting rollers rotated by contact with freely rotatable drive rollers whose orientations are changeable to cause the object-supporting rollers to rotate in one direction or another.
It is often necessary to divert objects from a conveyor belt, for example to another conveyor belt, for purposes of routing or positioning the objects for processing of one type or another.
Recently, conveyor systems have been developed in which the conveyor belt comprises a plurality of small, angled rollers that extend beyond the top and bottom surfaces of the belt. With such systems, objects carried by the conveyor belt, and more particularly by the rollers contained within the belt, can be diverted from the belt by rotating the rollers. The conveyor belt rollers can be caused to rotate using various methods. In one such method, the rollers are driven by selectively bringing a friction plate located beneath the conveyor belt into and out of engagement with the rollers. When the plate engages the rollers, the rollers are caused to rotate in response to the frictional forces between the friction plate and the rollers. In another method, free-spinning rollers located below the conveyor belt are selectively engaged with and disengaged from the conveyor belt rollers, and friction between the engaged rollers causes rotation of both sets of rollers in opposite directions.
Although the above-described conveyor systems provide significant advantages in relation to diverting objects from a conveyor belt, some limitations in their use still exist. For example, because the angles of the conveyor belt rollers are fixed, diverting can only be performed to one side of the conveyor belt and at a fixed diverting angle. Therefore, if it is desired to change the diverting direction or angle, the conveyor line must be shut down and the conveyor belt must be replaced with a different conveyor belt having rollers arranged in a different orientation.
A further disadvantage relates to roller slip. Specifically, when a friction plate is brought into contact with the rollers, the rollers must accelerate from zero angular velocity to a final angular velocity proportional to the speed at which the conveyor belt is traveling. Given that the rollers cannot instantaneously accelerate to the final angular velocity, roller slip occurs that causes wear to the rollers. The same phenomenon can occur, albeit to a lesser degree, in embodiments that employ free-spinning rollers to rotate the conveyor belt rollers. Specifically, although rotation of the free-spinning rollers reduces slip, slip can still occur during the period just after roller-to-roller contact is made.
Furthermore, when the friction plate or the free-spinning rollers are disengaged from the conveyor belt rollers, the conveyor belt rollers are free to rotate, which can enable objects present on the conveyor belt to drift across the belt. Although such drift may be desirable in some situations, it may be undesirable in situations in which it is desired to precisely control the lateral position of an object on the conveyor belt.